The present invention relates to a sampling apparatus and method, or more particularly to a sampling apparatus and method suitable for application to an automatic chemical analytical system of discrete action type.
In most of the conventional automatic chemical analytical systems, as disclosed in U.S. Pat. No. 4,298,570, a pipetting tube is cleaned only during the period after delivering the preceding sample into a reaction case before introducing another sample. The analytical system of single-line multi-analysis type, the use of which has recently been remarkably extended, also employs a similar cleaning operation.
In the case where one pipetting tube is used to perform the sampling operation for a plurality of analysis items in an ordinary analytical instrument, the pipetting tube is reciprocated between the sample absorbing position and the sample delivery position each time of introduction or absorption for an analysis item. The sampling of this method does not have high efficiency or speed in processing.
Accordingly, it is an object of the present invention to provide a sampling apparatus and method for an operation in such a manner that in the sampling operation from a sample cup to a reaction case by use of a pipetting tube, an accurate volume of a sample is distributed to a plurality of reaction cases with an increase of analysis items to be processed.
Another object of the present invention is to provide a sampling apparatus in which after introducing a volume of a sample designed for a plurality of analysis items into one pipetting tube at a time, sample portions of accurate amount are distributed sequentially to a plurality of reaction cases respectively.
According to an aspect of the present invention, there is provided a sampling apparatus comprising cleaning means including cleaning liquid exposed to contact the pipetting tube along the path thereof between the sample introducing position and the delivery position, so that the outer wall of the pipetting tube is cleaned by a layer of the cleaning liquid within a short time while passing through the cleaning means.
According to an embodiment of the present invention, even when a great amount of sample held in a pipetting tube is sequentially distributed to a plurality of reaction cases, the error in distribution amount is not increased, thus improving the sample-processing ability in practical applications. In fact, the sampling-processing rate is three times as high as that of the conventional systems. It has been found by the inventors that a serious problem is posed by the direct application of a new sampling method in which a sample is delivered in a plurality of parts after a single introduction thereof instead of in a single delivery following a single sample introduction as in the conventional methods. Specifically, the amount of the sample portion first delivered from the same pipetting tube is differentiated from that of the sample portions subsequently delivered therefrom. Experiments by the inventors show that the amount of the sample portion first delivered is always greater than that of the sample portions delivered for the second and subsequent times. This is found to be attributable to the fact that a small amount of the sample attaches to the outer wall of the pipetting tube. This problem has been obviated by the present invention.
In the case where a serum sample is introduced with the forward end of the pipetting tube dipped by 2 mm thereinto in a sample cup, the sample in the amount of approximately 0.1 .mu.l attaches to the outer wall of the pipetting tube. When the outer wall is cleaned, on the other hand, the sample attached to the forward end of the pipetting tube is diffused into the cleaning liquid. The cleaning liquid, normally, pure water instead of the sample, is attached to the outer wall of the pipetting tube. The only effect of this water in a reaction case is to dilute the reagent reacting with the serum. If water in the amount of 0.1 .mu.l is attached to the outer wall of the pipetting tube, for example, the reagent in the ordinary amount of 300 .mu.l is diluted only by 0.03%, thus having substantially no effect on the analytical accuracy of the automatic analytical system.
The above and other objects, features and advantages will be apparent from the detailed description taken in conjunction with the accompanying drawings.